1. Field of the Invention
The present invention relates to an internal-combustion engine control device for controlling an air-fuel ratio of an air-fuel mixture to be supplied to an internal-combustion engine (hereinafter referred to as the engine) and an ignition timing.
2. Discussion of Background
FIG. 45 is a block diagram showing one example of a prior-art engine control device. As shown in this drawing, fuel is drawn up into a fuel pump 2 from a fuel tank 1, restrained from pulsating by a fuel damper 3, cleaned of dirt and water content by a fuel filter 4, and kept at a constant pressure by a pressure regulator 5, then being supplied to a fuel injection valve 6.
Numeral 7 denotes a cold start valve for fuel injection to insure easier engine starting in cold climates.
Air that has passed through an air cleaner 8 is metered by an air-flow meter 9, and controlled of its flow rate by means of a throttle valve 10, passing through in an intake manifold 11 and being mixed with the fuel (into a mixture) at a fuel injection valve 6. The air-fuel mixture thus made is supplied into cylinders 12.
In these cylinders 12 the air-fuel mixture is compressed and ignited by a plug 13 at an appropriate timing. Exhaust gases flow in a manifold 14 and an exhaust gas cleaning device not illustrated and are discharged out into the atmosphere. Numeral 40 denotes an exhaust gas sensor which detects the concentration of exhaust gas composition (e.g., oxygen concentration).
Numeral 15 is a water-temperature sensor for detecting the temperature of engine cooling water; numeral 16 denotes a crank angle sensor built in a distributor for detecting the angle of engine crankshaft rotation; numeral 17 is an ignition system; and numeral 18 expresses a control device which controls the air-fuel ratio of the mixture to be fed into the engine and the ignition timing.
The crank angle sensor 16 outputs a reference position pulse at a crank angle reference position (every 180 degrees in a four-cylinder engine, and every 120 degrees in a six-cylinder engine) and also outputs a unit angle pulse every unit angle (for example every 2 degrees). Also, it is possible to know the crank angle by counting the number of unit angle pulses after the input of this reference position pulse within the control device 18.
The control device 18 consists of a microcomputer comprising, for example, a CPU (central processing unit), a RAM (random-access memory), an ROM (read-only memory) and an I/O interface. Receiving an intake air flow signal X1 from the air-flow meter 9, a crank angle signal X2 from the water-temperature sensor 15, a crank angle signal X3 from the crank angle sensor 16, an exhaust gas signal X10 from the exhaust gas sensor 40, a battery voltage signal not illustrated and a throttle full-close switch signal not illustrated, the control device operates in accordance with these signals, computing the quantity of fuel to be injected to the engine and the valve opening time of the fuel injection valve 6 and outputting an injection signal X5.
The fuel injection valve 6 operates, in accordance with this injection signal X5, once per engine rotation simultaneously with the operation of each cylinder, supplying a specific quantity of fuel to the engine.
The computation of the quantity of fuel injected (fuel injection time) Ti in the control device 18 is performed by the following equation. EQU Ti=Tp.times.(1+F.sub.t +KMR/100).times..beta.+T.sub.s ( 1)
where Tp is the basic quantity of fuel injected (basic valve opening time), which can be given by EQU T.sub.p =K.times.Q/N
where Q is the quantity of inducted intake air per rotation, N is an engine speed, and K is a constant.
Ft is a correction coefficient corresponding to the engine cooling water temperature; for example, the lower the cooling water temperature, the larger the value of Ft as shown in FIG. 46.
Also, KMR is a correction coefficient in high-load operation. It is used to read out for example, by a table look-up, values given on a data table as values corresponding to the basic fuel injection quantity Tp and the engine speed N as shown in FIG. 47.
Furthermore, Ts is a coefficient of correction by battery voltage, that is, a coefficient for correcting the fluctuation of voltage for driving the fuel injection valve 6; for example, the value of Ts is obtained from Ts=a+b (14=V.beta.), where V.beta. is the battery voltage and a and b stand for constants. As shown in FIG. 48, the lower the battery voltage, the larger the value of Ts.
.beta. is a correction coefficient corresponding to the exhaust gas signal X10 from the exhaust gas sensor 40. Using this .beta. can perform a feedback control of the air-fuel ratio to a specific value, e.g., a value near a theoretical air-fuel ratio of 14.8.
When, however, this exhaust gas signal X10 is used to make the feedback control, the air-fuel ratio of the mixture is always controlled at a fixed value; therefore the above-mentioned correction by the cooling water temperature and high load will become meaningless.
The feedback control according to the exhaust gas signal X10 is carried out only when the coefficient Ft of correction by the water temperature and the coefficient KMR of correction by the high load are zero.
In the meantime, the ignition timing control system of the engine has been proposed by, for example, Japanese Unexamined Patent Publication No. 59061/1982.
An electronic ignition timing control system is of such a constitution that the optimum values of spark advance corresponding to the engine speed N and the basic fuel injection quantity Tp are stored in advance in the form of a data table as shown in for example FIGS. 49 and 50, and the values corresponding to the engine speed and the basic fuel injection quantity are read out by a table look-up, so that the ignition timing may be controlled to the values by outputting the ignition signal X6 to the ignition system 17 to drive the ignition plug 13.
Since prior-art ignition control devices are constituted a stated above such that the quantity of fuel to be injected is determined in accordance with the basic quantity of fuel injection and the engine speed, that is, in accordance with the quantity of intake air and the engine speed, the correction of the quantity of fuel injection under a high-load condition depends entirely upon an open-loop control system. Therefore, the output torque obtained is not necessarily the maximum output torque that the engine can produce.
The air-flow meter 9, the fuel injection valve 6, or the internal-combustion engine itself is subjected to variations and changes with time, with the result that initially matched optimum air-fuel ratio and optimum ignition timing will become not suitable for producing the maximum output torque.